Prestressed sucker rod



Nov. 2, 1948. P. F. ROSSMANN 2,453,079 PRESTRESSED SUCKER ROD V Filed Aug. 5,-1944 INVENTOR. PETER F. ROSSMANN ATT URN EY' Patented Nov. 2, 1948 UNITED! ,STATE S, PATENT OFFICE 3 a Ifaisao'is a p f PRESTRESSED SUCKER BOD Peter F. Bossmann, Morristown, N. J. Application August 5, 1944, Serial No. 548,291

2 Claims.

deformation imposed thereon to increase its tenysile strength and also to extend fatigue life. i i

In connection with the embodiment of the invention in alsucker rod or similar articlewhere it is subjected while in use to alternate and recurrent tensile and compression stresses .as in oil well pumping, it is known that the resultant stretch or elongation of such sucker rods is an undesirable factor. withregard to the attaining of the requisite pumping and also infiuences the depth since the elongation produces waves in the rod especially when the depth is great; The speed of pumping is also a factor contributinggto the short life of suchrods. i

The present disclosure-features a method of treating sucker rod sectionsand like length of rods by stretching the same to place. the rod under a predetermined axial deformation, retaining the elongation stresses so produced within the rod to resist further elongation of the rod within, the limits of retained stresses, and thereafter to restrain any tendency of the rod to revert to its initial configuration during use. i

Preferably. the degree of deformation to which the rod is subjected is limited topobtain the best results, for it hasbeen found that the stresses can be increased even beyondnormal magnitudes by restraining the stress cycle to a very small stress range. For instance; inthe case of sucker rods, the stress may be first changed from zero to 100,000 pounds per square inch and the fatigue life will be less than if the change were made subsequently from, say,80,000 to 100,000 pounds per square inch by reason of conditions imposed thereon during use. i 1

Various other objects and advantages of the invention will be in partobvious from a consideration of the method features of the disclosure (and from an inspection of the accompanying drawings) and (in of one method of practicin-gthe invention and the inven ion a so ge e in g risin new and 2 novel modifications of the preferred method (and other featuresof construction and combination of parts) hereinafter set forth and claimed.

In the accompanying drawing: 1 t Figure 1 is a portion of asectional suckernrod illustrating in axial cross. section a unit constituting a preferred embodiment of the invem tion and shown attachedto the next two similar sections. In the several figures the mid-portions are broken away to reduce the length show ing of the sections.

Figure 2 is a view in axial section of the componentparts of the unitforming Figure ll with its tension rod in its normal condition before it is stretched; and of the compression sleeve prior to being rolled intoplace, located in telescopic relation and illustrating .the first step in the method of forming the complete article shown in Figure 1. j i a t Figure 3 is a similar view of the parts shown in Figure 2 with the outer sleeve almostin its part will bemore fully set forth in the following particular description final position and illustrating the next step in the method of forming the. completed showing in Figure 1. i 1 v Figure 4 is a longitudinal sectional view of.:a modified. form of sucker rod section and which may be regarded as illustratingthe component dition; and l Figure 5 is a similarviewof still another modification.

In the drawings and referringfirst to Figure 1, there is disclosed a suckerfrod l0 formedof a plurality of similar units or sectionsll. .Each

section-includes a pair of telescoped elements.

hereinafter sometimes referred to as an inner tension element. orcore I2 and an outercompression element or sleeve 13.

Referring to the tensionelement l2 as illustrated in its original or unstressed condition shownin Figures Zand. 3, there is disclosed a solid metal rod [2a, preferably of alloysteel,the midlength portion M of which is of a cross sectional area reduced from that of the end portions l5 and I6 toform the mid-portion as a long, relatively thin shank. Opposite ends of the shank coact with the adjacentenlarged end portions to form a pairv of inwardly facing stop shoulders I1 and i8, disposed in parallel planes at right angles to the axis of the core element. The end portion 15 is provided with a threaded socket l9 and'the opposite end portion is reduced and forms an externally threaded stud-20. As

shown in Figure 1, the stud of one section is designed to be threaded into the socket of the next adjacent section and a number of these sections coact to form a completed sucker rod following conventional practice in this respect.

It is a feature of this disclosure that the tension element I2 be slightly prestretched, as, for

- instance, from the distance measured between the planes a--b' and c'-d' in Figures 2 and 3 to the increased length defined by the distance between the planes a-b and c-d, of Figure 1. This stretching is attained by simplypulling the ends of l 2a apart and thus away from each other as indicated by the double-headed arrow of Fig-- ure 1.

tially all of the compression rod 24 and the outer end of the bore 30 is internally threaded as shown at 3 i. The two bores are separated by an internal The tube I3a from which the sleeve i? is formed has initially an internal diameter sufli cient to permit it to slip over the enlarged end portions IE or 46 and has a length slightly less than the axially measured distance between the,

stop shoulders Ill-48 as seen in Figure 2. In order to bring the tube lea, into the reduced length of the finished form, it is subjected to a conventional tube reducing rolling operation under pressure sufficient to cause the tube finally to engage snugly the shank 3 with such axial elongation as will cause the ends 2! and 22 of the tube to bear against the stop shoulders l1-l8 and in this way force them apart. Following conventional tube rolling operations, the squeeze rollers of a forming machine operate first on the two ends ccnstrictmgthe same to- I wards the core provided by the shank portion of the stock [2a somewhat as suggested by the exaggerated showing in Figure 3. In the'showing in Figure 3 it is assumed that the outer tube is just touching at its opposite ends, both the adjacent ends of the shank and the outer portions of the two shoulders. As the deforming rollers move from the ends of the tube towards the center they will effect a crowding of the tube vforcefully in outward directions against the shoulders .to force them apart and thus place the shank portion of rod 92 under tension pan ticularly in the portion thereof between the planes a-b and cd. At the same time, while the inner member I4 is thus being deformed axially under tension, the rolling operation will deform the outer tube i3a under compression. In the resulting article as shown in Figure 1, the major portion of the core [2 is held .withits stress trapped therein entire length of which is held with its stresses trapped therein by being squeezed between the shoulders I1 and-l8 of the tension element 12.

While it is most convenient to use the shank as a mandrel on which to roll the tube, it is obvious that the tube need not snugly encircle the shank; it is simply necessary that it fit between and force apart theshoulders lil8. It K's-within the scope of the disclosure to first stretch the core element l2 to deform the same axially and then roll the outer sleeve into place between the'shoulders 3 either with the tube undeformed or preferably, deformed axially under compression before it is rolled into position betweenthe shoulders.

Referring to the modified form of the invention shown in Figure 4, here again the unit forming the sucker rod section 23 is formed solely of two telescoped elements 24 and 25,-oi which the inner element'24 will sometimes hereinafter be referred to as a compression rod and the outer element 25 will be referred to as a tension mom'- =ber. The compression rod 24 is of one piece and comprises a long cylindrical portion 26 which constitutes the major portion of its length. The

by the outer sleeve 83, the

partition 32 which provides a stop wall surface 33 constituting the bottom of the bore 30. The surface 33 is engaged by the inner rounded end 34 'of the compression member 24. The stud 21 is in threaded engagement with the threads at 3| and the stud is so dimensioned that when the parts are in their final stressed position as shown in Figure 4, the portion of the stud which protrudes outwardly beyond the adjacent end of the tension member corresponds in size and function to the stud '20 of the preferred form. The stud 21 is provided at its outer end with a kerf 35 designed to be engaged by a screw driver or similar tool for rotating the compression" member into bearing engagement against the stop wall surface of the tension member.

In operation, it will beunderstood' that the compression member 24 with its initial unstressed and natural dimensions is inserted with its long cylindrical end'in-advance into the bore 311 and then by means of a-turning tool engaging the kerf, the compression member is forced hard into engagement with the surface 33' of the wall 32 with a torque sufficientlyto develop compression strains in the compression or core member 24 as indicated by the double-headed arrow inFigure 4. In its reactory-tendency to elongate the portion'of tension'inember 25 between the stops provided by the partition 32 and the outer threadedend, the tension membe'rfifi is elongated and thus placed under'tension. It will be seen from this construction that having so deformed both members axially, the inner core element under compression'and the outer tubular element under tension, the parts will tend mutually to resist reversion of each other conditions;

'Referring to the second modified form of the invention shown in Figure 5, the disclosure resembles that of the section II shown in Figure l with corresponding parts having the same reference characters. In this case theend portion 16 has been omitted; stud 20 slightly elongated and a nut 38 threaded on stud 20 for bearing engagementwith the adjacent end 37 of the sleeve [3. The nut may beregarded as an equivalent of the end portion IS with the additional advantage that it' is adjustable andtheinner face l8 of the nut may be considered as the equivalent of the shoulder l8. I In this modification the sleeve is disclosed as optionally having a loose fit on the core l2 and the tube, even in its initial unstressed form, need not have an internal diameter greater than the enlarged end for it may be slipped onto the smaller end of the core 12 before the nut is locatedin place. In Figure 5 the nut may be preset at any point desired and sleeve l3 may be rolled into position endwise on stop shoulders I 1 and I8 as has been described for the Figures 1-3 formof the invention. Otherwise the unstressed sleeve may be located in place and the'nut turned hard to their initial unstressedagainst the tube end 31. As the nut is advanced after contact there will be developed a resulting deformation of the core member I! under axial tension and an equal deformation of the sleeve 13 under axial compression as indicated by the headed arrows.

In the case of the preferred form of the invention'as shown in Figure 1 and in the modified form shown in Figure 5, the axially squeezed restraining sleeve [3 will, by reason of its compression, act to restrain the tendency of the tension member 12 to revert to its length dimension when it was in its unstressed condition such as is shown in Figure 2. When the elements are prestressed as herein indicated, the stress characteristics will of course be limited in the Figure 1 showing between the shoulders 11-18; in the Figure 4 showing between the wall 33 and the threaded portion 3| and in the Figure 5 showing between the shoulders I! and the nut 36. While the end portions are unstressed, they are relatively short compared to the over-all length of the section and besides are usually more massive than the shank portion therebetween and are thus less liable to disintegrate under prolonged fatigue. It will be noted that in all'cases the entire section is within the axially projected outline of the parts which form the joints between adjacent sections as shown in Figure 1 so that the addition of the second element does not increase the presently known cross sectional area of conventional form of sucker rods or add mutually to their cost.

By utilizing composite rods of the characters illustrated, the tendency of the rods as a whole to elongate in use has been largely eliminated so that the rods at the end of an operation on which they are transmitting loads axially therethrough, even when the loaded transmissions are rapidly reversing themselves, will maintain their original lengths, and by reason of this elimination of rapidly recurring changes in internal stress conditions, the life of the rods is materially lengthened.

In the case of using the instant form of sucker rod sections, there has been eliminated, or at least reduced, the rapidly succeeding waves of compression and tension stresses so objectionable with known forms of sucker rods when used in deep well pumping or the like.

I claim:

1. A sucker rod section provided at opposite ends with elements of fastening means for securing the section to other similar sections to form a complete sucker rod, said section including a pair of elongated telescoped elements permanently secured together, each element formed integrally as one piece, one constituting a solid core element defined at opposite end portions with enlarged heads and forming therebetween a shank portion integral with the heads and of less cross section than its headed end portions, said shank portion forming with the said headed end portions a pair of inwardly facing non-rotative stop shoulders, said core element in the portion thereof between the shoulders beinggdeformed under apreimposed tension and with the headed end portion not necessarily stressed-the other element constitutin a retaining sleeve. deformed under, compression, fitting between the shoulders with its ends in fixed bearing engagement against the shoulders and acting resilientlyil a tendency to spread them apart,and the said two elements at all times reacting on each other to maintain the elements so formed into theirrespective compressed and tensioned stress conditions and thus each acting to resist the returnof the other to its initial length before it was deformed.

, 2. A composite sucker rod section having an.

inner core member provided "with connecting means at its ends permitting a plurality of sections to be connected together to form a sucker rod of determinate length, spaced shoulders on said inner number extending radially outward adjacent each end thereof, a continuous outer tubular member surrounding said core member between said shoulders and bearing against said shoulders at its endsso as to maintain said core member under tension and said outer tubular member under compression irrespective of the rod section being connected to another section,

whereby further elongation of said sucker rod section in operation is substantially prevented. PETER F. ROSSMANN.

REFERENCES orrnn .The following references. are of record inthe I file of this patent:

UNITED STATES PATENTS Certificate of Correction Patent No. 2,453,079. November 2, 1948 PETER F. ROSSMANN It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 6, line 27, claim 2, for the word number read member;

and that the said Letters Patent should be reedwith this correction therein that the same may conform to the record of the case in thePatent Ofiice.

Signed and sealed this 29th day of March, A D. 1949.

THOMAS F. MURPHY,

Assistant Uommissianer of Patents. 

